Among wheel loaders, some are installed with a so called HST (Hydro Static Transmission). An HST type wheel loader, drives a hydraulic pump using an engine, and drives a hydraulic motor for travel using the hydraulic fluid ejected from the hydraulic pump. Because of this, the wheel loader travels. In such an HST type wheel loader, by controlling the engine rotational speed, the displacement of the hydraulic pump, the displacement of the hydraulic motor for travel, and the like, it is possible to control the vehicle speed and the traction force (see Japan Patent Laid-open Patent Publication JP-A- 2008-144942).
In the above wheel loader, an operator can select the execution of traction force control. In traction force control, for example, the displacement of the hydraulic motor for travel is restricted to an upper limit displacement that is less than the maximum displacement. Because of this, the maximum traction force is reduced. The operator, when the phenomena of slipping or stalling occur due to the traction force being too large, selects the execution of traction force control. Because of this, the maximum traction force is reduced, and the occurrence of the phenomena of slipping or stalling or the like is suppressed.